Involuntary movements have often been difficult ot classify clinically. Clinical and physiologic analysis of a continuing series of patients has led to new classifications and pathophysiologic insights. Patients with myoclonus have been studied to seek further understanding of this confusing involuntary movement. Extensive studies have classified most cases seen within previously identified categories. We have studied and characterized physiologically three patients with tremor that have had cortical myoclonus and fit the disorder of cortical tremor. Physiologic studies of essential tremor and parkinsonian tremor using transcranial magnetic stimulation have shown that both tremors can be reset by direct brain stimulation. This gives further information about the nature of the central generators of these tremors. Extensive clinical and physiologic studies have been completed in patients with palatal tremor (myoclonus). We have further data confirming the division of these patients into two groups: idiopathic and secondary. A study of movement-related cortical potentials in patients with dystonia (hand cramps) have revealed an abnormality of cortical activation. A physiologic investigation of facial twitching seen in patients with olivopontocerebellar atrophy has revealed that this disorder is a form of myoclonus. The disorder probably results from brain stem degeneration. Positron emission tomography (PET) studies of essential tremor using region cerebral blood flow have confirmed our earlier observations using glucose metabolism and implicate the cerebellum and its pathways in the genesis of this disorder.